1. Field of the Invention
This invention relates to a device which detects optically and continuously an inter-vehicle distance between a car and a preceding car.
2. Discussion of Background
Formerly, as a distance detecting device of this kind, there are disclosed for instance Japanese Examined Patent Publication Nos. 380085/1988 and 46363/1988. Hereinafter, explanation will be given to FIG. 4. Numerals 1 and 2 signify a couple of optical lenses disposed on the left and on the right. In the signal processing unit 20, an image obtained from the image sensors 3 and 4 is shifted and superposed on another image. Finally the shift quantity "a" is obtained in which both images agree the most. The distance R to the object 21 is obtained by the following equation utilizing the principle of triangulation from the shift quantity "a". ##EQU1## where f is the focal length of the lenses 1 and 2, and L is a base length between the lenses 1 and 2.
Furthermore, as an image tracking method of the preceding car taken by the image sensor, there is disclosed in for instance Japanese Examined Patent Publication No. 33352/1985. In this case, the above target is image-tracked by a method in which an operator looks at a display and sets a tracking gate (window) encircling a target to be tracked on the display.
In an inter-vehicle distance detecting device which continuously detects the inter-vehicle distance between a driving car and the preceding car to be tracked by combining an optical distance detecting device which utilizes image sensors and an image tracking device for a preceding car as mentioned above, as disclosed in the above Japanese Examined Patent Publication No. 33352/1985, it is almost impossible for a driver to set-up a window having a similar shape with the preceding car image, by using a joy stick, a track ball, or a mouse while driving the car.